Television pictures broadcast that evening showed the majority of placards in similar handwriting. One of three veiled women - or at least people who appeared to be women - was seen writing placards and distributing them. Most were held by men who had also hidden their identity.

Among the slogans were "Europe, your 9/11 will come" and, in an apparent reference to the four July 7 suicide bombers, "Europe you will pay, fantastic 4 are on their way". One protester was dressed as a suicide bomber.

The only arrests were of two counter-demonstrators, who police said were held after apparently attempting to hand out caricatures of Mohammed. Both were released without charge after a few hours.

Inayat Bunglawala, a spokesman for the Muslim Council of Britain umbrella group, said last night: "The placards were quite disgraceful and seemed to constitute a clear incitement to violence, even murder."

He told Channel 4 News: "I think the police were right to take footage of the event and identify the ringleaders, because although several hundred people were there the placards were being held by a tiny group of extremists.

"I think people will understand that the police did not step in to make matters worse and were waiting for a more propitious time to charge these people. Most Muslims feel enormous distress and anguish at what has occurred. There will be no sympathy for [the extremists] when they are charged by the police."

A mob of 20,000 attacked Denmark's consulate in a Christian neighbourhood of Beirut yesterday. Denmark urged its citizens to leave Lebanon as soon as possible. On Saturday Syrian demonstrators set fire to the Danish and Norwegian embassies in Damascus.

Iran's foreign ministry said it had joined Syria, Saudi Arabia and Libya in withdrawing diplomats from Copenhagen, while there were also protests in Afghanistan, Egypt and Turkey. Arla Foods, a Swedish-Danish company, said it was losing $1.8 million worth of sales a day in the Middle East. Its products were removed from shelves in Saudi Arabia, Qatar and Kuwait.

Jack Straw, the Foreign Secretary, and Peter Hain, the Northern Ireland Secretary, led Government appeals for calm but stopped short of endorsing Tory calls for the police to arrest militant protesters in future.

He said the violence, particularly the burning of Danish missions, was "totally unjustified and what we want to see is this matter being calmed down".

He praised the vast majority of Muslims in Britain who had protested peacefully and said it was "extremely impressive" that Muslim organisations had condemned the violence and the threats of violence.

Mr Hain called on all sides to "cool it" and said that politicians must not try to "second guess" police: "If people are on our streets inciting terrorism or promoting suicide bombings, they should be dealt with and dealt with toughly and firmly - and they will be.

"But that is the police's responsibility and they will discharge that."

David Davis, the shadow home secretary, said that slogans such as "Massacre those who insult Islam" amounted to incitement to murder and that police should take "a no tolerance" approach to them. He told the Sunday Telegraph:"Clearly, some of these placards are incitement to violence and indeed incitement to murder." Dominic Grieve, the Conservative legal affairs spokesman, expressed concern that it could prove impossible to identify those responsible because arrests had not been made at the time.

Scotland Yard, which has received at least 100 complaints from members of the public so far, defended the decision not to make arrests. It said the officer in charge at such scenes had to weigh the need to make arrests against the likelihood of provoking more serious unrest.

All complaints would be passed to the public order crime unit for further investigation. A spokesman said: "We have stated that arrests if necessary will be made at the most appropriate time.

"This should not be seen as a sign of a lack of activity. Specialist officers were deployed to record any potential event, should it be needed at any point in the future." She said the Crown Prosecution Service was responsible for deciding whether to press charges.